I was in a game with 2 medics 1 Sp weapons and me as Tech. We were doing great, until we got to a mission that required at least 1 Flamethrower. Everyone got the Flamethrower, even the medics who switched classes. One guy got hit by a Parasite, and guess how it ended. In the second try those guys went back to Medic and we beat the level without any Parasites hatching. Parasites are really easy to avoid since they first need to hatch.